Conventionally, stereoscopic vision which produces stereoscopic effect by presenting different images to the left and right eyes have been studied. For example, a technique called autostereoscopy have been widely known, which produces stereoscopic effect by arranging images viewed from left and right viewpoints, side by side, and viewing the image for right-eye through the right eye and the image for left-eye through the left eye while the user is defocusing their eyes.
Techniques for autostereoscopy include parallel viewing technique described with FIGS. 7(a) and 8(a) and crossed viewing technique described with FIGS. 7(b) and 8(b). In the parallel viewing technique, a stereoscopic image having a left-eye image 31 and a right-eye image 32 arranged on the left and right, respectively, as shown in FIG. 7(a) is viewed in such a manner that the right eye views right-eye image 32 arranged on the right and left eye views the left-eye image 31 arranged on the left with their focal points adjusted at a point more interior than the image, as shown in FIG. 8(a). In crossed viewing technique, a stereoscopic image having an left-eye image 31 and an right-eye image 32 arranged on the right and left, respectively, as shown in FIG. 7(b) is viewed in such a manner that the right eye views right-eye image 32 arranged on the left and the left eye views left-eye image 31 arranged on the right with their focal points adjusted at a point before the image, as shown in FIG. 8(b).
Also a 3D display which provides stereoscopic vision using binocular parallax by placing a slit plate 34 in front of a liquid crystal panel 33 as shown in FIG. 9(a) has been developed. Specifically, as shown in FIG. 9(b) a displayed image 35 for 3D display, which is composed of images for left and right eyes, arranged alternately, is displayed on liquid crystal panel 33, and when the image is viewed over slit plate 34, left-eye image 31 can be viewed by the left eye and right-eye image 32 can be viewed by the right eye.
A displayed image for 3D display is prepared by synthesizing left-eye and right-eye images in accordance with the specification of the slit plate. For example, if the width of the apertures and that of shading portions of the slit plate used for a 3D display are equal to one pixel-width of the liquid crystal panel, pixels in odd-numbered columns of the left-eye image and pixels in even-numbered columns of the right-eye image are picked up and arranged side by side alternately, forming a displayed image for 3D display, as shown in FIG. 10.
Since there is no particular stereoscopic image format defined for general purposes, as the methods frequently used for storage of a stereo image, in some cases the left-eye image and the right-eye image are stored as separate image files with a separate record of the correspondence between the left-eye image and the right-eye image for the stereoscopic image; in other cases a single image in which the left-eye image and the right-eye image are arranged left and right and synthesized is stored as a stereoscopic image format.
Particularly, since the latter format is easily viewed in autostereoscopic mode when it is displayed with usual 2D image display software, this is widely used as a stereoscopic image format. However, this format has the problem that it is impossible to determine whether the format made up of images arranged left and right is for crossed viewing mode or for parallel viewing mode, at a sight of the images.
Further, if an unskilled person without knowledge of stereoscopic vision handles such format images arranged left and right to display on a usual 2D display, they may take it for device failure since akin images are displayed side by side; or if the image doubled in width compared to a normal 2D image because two images are arranged left and right, is printed by a printing service for digital camera images, the central part of the images arranged left and right is trimmed and printed, possibly causing a feeling that the printing service is problematic.
As a counter measure to solve the above problems, it is preferable to provide a means for making the user understand such an image as a stereoscopic image at a glance, by adding information that indicates the entity of a stereo image within the image. For example, the invention disclosed in Patent document 1 proposes a method of adding distinction information of left and right below the images, by mounting a stereoscopic adapter to a camera when a stereoscopic image is shot by the camera.
Patent document 1:
Japanese Patent Application Laid-open Hei 9-160143